Harkness (1991b)
first carried out light-curve calculations that took into account the
dependence
of the opacity on temperature, density, and composition, and he found that
the light curve of model W7 was about right for normal SNe Ia. Machinery
developed for calculating gamma-ray deposition
(Höflich et al
1992)
and bolometric and monochromatic light curves
(Höflich et al
1993)
led to a major computational effort by
Höflich &
Khokhlov (1996),
who calculated local thermodynamic equilibrium (LTE) light curves for 37
explosion models encompassing each of the kinds mentioned above. The light
curves and colors of Chandrasekhar-mass carbon-ignitor models depend mainly
on the amount of 56Ni that is ejected: Models with more
56Ni
are hotter and brighter, and, because the opacity increases with temperature
in the range of interest, they have broader light curves. Carbon-ignitor
models can account reasonably well for the photometric properties of both
normal and peculiar weak SNe Ia
(Wheeler et al 1995,
Höflich et al
1996,
1997),
with normal SNe Ia requiring MNi 0.6
M
(Figure 12) and SN 1991bg requiring only about
0.1 M.
The differences
between the calculated light curves for different kinds of carbon-ignitor
models that eject similar amounts of 56Ni are fairly subtle, so
deciding just which kind of explosion model applies to any particular SN
Ia on the basis of its light curves and colors alone is difficult.

Discriminating between carbon ignitors
and helium ignitors is more straightforward because they have such different
compositions.
Höflich &
Khokhlov (1996)
found their helium-ignitor models to be inferior to the carbon ignitors in
producing the light curve and colors of a normal bright SN Ia. The helium
ignitors do not work at all for subluminous SN Ia like SN 1991bg because the 56Ni in the outer
layers keeps the photosphere hot and the colors too blue.